G. J. Galvin

Co/GaAs interfacial reactions

The reactions of metals with GaAs are substantially more complex than comparable metal‐silicon systems. In this paper, phase formation in the Co‐GaAs system is examined in detail and contrasted with other metal‐GaAs and metal‐silicon systems. Both elemental and microstructural characterization techniques are used, and the limitations of each are discussed. Cobalt begins to react with GaAs at 375u2009°C and initially forms a ternary phase of approximate composition, Co2GaAs. Subsequent reactions or higher‐temperature annealing results in the formation of binary phases CoGa and CoAs. The observed phase formation is controlled by the species with the largest diffusion coefficient, and this species is determined by the temperature. At sufficiently high annealing temperatures, arsenic is lost from the surface, and an epitaxial CoGa phase is formed on the GaAs.

Melt dynamics of silicon‐on‐sapphire during pulsed laser annealing

Transient electrical conductance measurements have been made on 0.45‐μm silicon‐on‐sapphire during pulsed laser annealing with 25‐ns ruby irradiation. The photoconductive contribution to the transient current was sufficiently small that the entire melt and resolidification process could be directly observed. The technique yields quantitative measures of melt depths, melting velocities (5–13 m/s), and solidification velocities (2.8–3.3 m/s). Combined with the complementary techniques of time‐resolved reflectivity, energy transmission, and calorimetric energy absorption, transient conductance provides a powerful new diagnostic for investigating melt dynamics.

Solidification kinetics of pulsed laser melted silicon based on thermodynamic considerations

The measured solidification velocities in silicon after pulsed laser melting are analyzed in terms of thermodynamic and kinetic considerations. Both interface and thermal transport limited growth regimes are observed. From the observed kinetics in the 1–6‐m/s regime, the undercooling at the liquid‐solid interface can be calculated. At velocities ≤6 m/s the undercooling increases with interface velocity at the rate of 15±5 deg/m/s.

Phase formation and reaction kinetics in the thin‐film Co/GaAs system

The solid state reaction between a Co thin film and (100) GaAs was investigated using Rutherford backscattering spectrometry. At 400u2009°C a reacted layer of composition Co:Ga:As=2:1:1 was observed to form. This reaction product obeys diffusion controlled growth kinetics and maintains its composition for annealing (400u2009°C) from 15 min up to 24 h.

Solid phase epitaxy of deposited amorphous Ge on GaAs

Solid phase epitaxial growth of electron beam deposited amorphous germanium on GaAs has been obtained. Contamination at the Ge/GaAs interface is observed to impede and even prevent epitaxy of the deposited Ge layer. Complete epitaxy of the Ge was obtained by thermal annealing (400u2009°C for 1 h) of layers deposited on in situ sputter cleaned GaAs substrates.

Transient Conductance Measurements During Pulsed Laser Annealing

Measurements were made of the conductance of single crystal Au-doped Si and silicon-on-sapphire (SOS) during irradiation with 30 nsec ruby laser pulses. After the decay of the photoconductive response, the sample conductance is determined primarily by the thickness and conductivity of the molten layer. For the single crystal Au-doped Si, the solid-liquid interface velocity during recrystallization was determined from the current transient to be 2.5 m/sec for energy densities between 1.9 and 2.6 J/cm 2 , in close agreement with numerical simulations based on a thermal model of heat flow. SOS samples showed a strongly reduced photoconductive response, allowing the melt front to be observed also. For complete melting of a 0.4 μm Si layer, the regrowth velocity was 2.4 m/sec.

Applications of Energy Beams in Material and Device Processing

Energetic ion beams used outside the traditional role of ion implantation are considered for semiconductor applications involving interface modification for self-aligned silicide contacts, composition modification for formation of buried oxide layers in Si on insulator structures and reduced disorder in high energy ion beam annealing for buried collectors in transistor fabrication. In metals, aside from their use in modification of the composition of near surface regions, energetic ion beams are being investigated for structural modification in crystalline to amorphous transitions. Pulsed beams of photons and electrons are used as directed energy sources in rapid solidification. Here, we consider the role of temperature gradients and impurities in epitaxial growth of silicon.

Melt Depth And Regrowth Kinetics In Pulsed Laser Annealing Of Silicon And Gallium Arsenide

High intensity pulsed laser irradiation of semiconductor materials results in ultra-fast melting and resolidification of a thin surface layer. An experimental probe has been developed based on the discontinuous change in electrical conductivity of a semiconductor material upon melting. Real time monitoring of the dynamics of pulsed laser melting and resolidification can be obtained by transient electrical conductance measurements. Melting velocities from 5 to 200 m/s and resolidification velocities of 1 to 20 m/s have been observed in silicon with this technique. Simultaneous measurement of the optical reflectance provides additional complementary information on laser melting dynamics. Data from both electrical conductance and optical reflectance measurements are presented for silicon and gallium arsenide. The real time experimental data provide strong evidence for a simple thermal model for melting and resolidification during nanosecond pulsed laser annealing.